1. Field of the Invention
This invention relates to a method of producing a semiconductor device having a small electrostatic capacitance relative to the ground and a short delay time realized by such small capacitance to the ground, so that the operating frequency band width of the device is broadened and the operating speed of the device is increased. In the method of the invention, a semi-insulating semiconductor substrate is formed by generating crystal lattice defects therein through irradiation, and the semiconductor device is produced by using the surface part which is made semiconductive, of the thus formed substrate.
2. Description of the Prior Art
To broaden the operating frequency band width of a semiconductor device such as a transistor and an integrated circuit and to increase its operating speed, the propagating time of carriers in the semiconductor device should be minimized by reducing the dimension thereof, and furthermore it is very important to suppress the delay time due to the electrostatic capacitance of the semiconductor device relative to the earth.
To this end, in the case of using silicon semiconductor, it has been tried to form the substrate in the form of SOS (silicon on sapphire) structure, SIMOX (separation by IM plated oxygen) structure, graphoepitaxial structure, or gold-diffused silicion substrate. In the case of using a compound semiconductor, the semiconductor device structure is formed by making the substrate semi-insulating by adding an impurity at a high concentration and producing an epitaxial layer on that substrate, which epitaxial layer has a specific resistance of similar magnitude to that of a regular semiconductor.
The aforesaid SOS structure, which uses epitaxial growth of a silicon layer on a sapphire substrate, has shortcomings in that stress is caused in the silicon layer due to the fact that the crystal lattice of sapphire does not match with the lattice of silicon and in that the sapphire substrate is costly. Thus, the SOS structure has problems in the techniques for manufacture thereof and the cost thereof.
The SIMOX structure, which uses the growth of a silicon oxide (SiO.sub.2) film in a silicon substrate by implanting oxygen into the silicon substrate at a high concentration and then annealing at a high temperature, has shortcomings in that the surface of the silicon substrate is susceptible to comparatively large damage, so that it is necessary to grow an additional epitaxial layer on the surface thereof. Thus, the SIMOX structure has drawbacks in its complicated manufacturing process, the need to implant a large amount of ions which requires a long working time, and its high cost.
The graphoepitaxial structure, which uses the growth of a single crystal silicon layer by forming fine grooves on a glass substrate, producing a polycrystal silicon layer while using said grooves as seed crystals, and converting it into the single crystal silicon layer by light or short thermal annealing, has shortcoming in that the coefficient of thermal expansion of the silicon layer is different from that of the substrate.
The gold-diffused silicon substrate structure, which uses diffusion of gold in silicon to increase the resistivity of silicon and ion implantation therein for producing an active surface layer, has shortcoming in that the diffused gold tends to introduce contamination during the formation of a semiconductor device.
In the case of compound semiconductor such as gallium arsenide (GaAs), a large amount of chromium or the like is introduced into a substrate for rendering the substrate semi-insulating, resulting in a shortcoming in that the presence of such chromium or the like tends to introduce contamination during formation of an active layer on the substrate by epitaxial growth.